There is known a method for connecting a conductor enclosed by a flowable insulation to a copper terminal pin coated with a tin-lead alloy (cf., U.S. Pat. No. 3,627,970, published 1971), whereby a conductive connection is formed through heating a point by a heated tip of a tubular electrode. However, such a connection involves soldering and the above method fails to provide successive connection of more than one conductors to the same terminal pin in close proximity to one another.
Also known is a method for connecting an insulated conductor to terminal pins of a printed circuit board (cf., U.S. Pat. No. 3,673,681, published 1972), whereby an insulated conductor is connected by resistance welding involving one pulse of welding current to be passed therethrough. The insulation of the conductor is pressure-deformable by the electrode. A disadvantage of this method resides in the use of high-cost nickel conductors and gold-plated stainless steel terminal pins; it is also very labor-consuming.
Further known is a method of forming a connection between members coated with flowable insulation, whereby the members are pressed together by the electrodes followed by the application of three current pulses through the electrodes. The first pulse acts to melt the insulation, the second pulse effects a weld between the members, and the third pulse effects a cleaning action, the third pulse being triggered and quenched subsequent to raising the electrodes from the welded members to clean the electrodes of the flowable insulation (cf., U.S. Pat. No. 3,263,059, application filed 1963).
Inherent in the above method is a disadvantage in that the edges of the thus formed weld are covered with sharp clusters of solidified flowable insulation extending upwards from the surface of the welded members and affecting the accuracy of alignment in connecting subsequent members thereto. In addition, the method provides a relatively low strength of such welded couples as copper terminal pin-insulated copper wire, amounting only to about 20-25% of the strength of the insulated wire.
The sharp clusters of flowable insulation are formed due to raising the electrodes at a point when the temperature of the electrodes and the members being welded is substantially less than the melt point of the flowable insulation. This occurs after the second current pulse is passed and subsequent to a dwell time necessary for completing the weld.